Innovation in Airport Vehicles

Aircraft take-off, landing and preparatory operations constitute the purpose of airports, and aircraft themselves dominate activity on airports’ runways, taxiways, concourses and hangars, winged giants over their host of attending ground vehicles. These airport vehicles, in their great variety, though remain essential for flight and for the well-synchronized sequences of aircraft operations at the modern airport. The variety, which exceeds that of the aircraft they serve, reflects the complexity of the
modern aircraft.

Airport vehicles comprise those that tow aircraft; service aircraft, including fuel and de-ice; load freight and transport
passengers; provide emergency including fire-fighting services; and clear runway and taxiway surfaces, including from snow and ice and finally also includes cars, vans and motorcycles. The vehicles range from those specially designed and unique to airports to those only slightly modified from the world outside the airport, from the technologically complex to the simple. This article looks at developments in technologically advanced airport vehicles.
 
Tow Tractors

Aircraft represent the maturation of technology for flight, in contrast to ground operations, in which they lumber on relatively small wheels by the inefficient means of jet thrust. To their aid come tow vehicles, specially designed, as displayed in the musculature of more capable models with big wheels and small low bodies, to move aircraft between positions on the runways and concourses and hangars, i.e. in pushback, gate-to-gate and maintenance towing. Initially tow vehicles transmitted the towing force via a towbar coupled to the aircraft’ nosewheels. The vehicle’s weight provided traction for the movement and heavier aircraft required heavier tow vehicles and indeed the Airbus A380, which could weigh almost 600t, would require a 70t tractor of this type for safe towing.

More advanced vehicles, towbarless tractors lift and position the nosewheel on a platform on the tractor. These vehicles can weigh less, since the nosewheel weight provides traction for movement, and tow at higher speeds and also offer greater economy and safety. The advent of the A380 led to the need for tractors more capable than those then existing and a number of manufacturers took the towbarless approach and, by also introducing new technologies, produced the most advanced aircraft tow vehicles in the world.

Technologies on advanced towbarless tractors include a hydrostatic all-wheel drive system, which produces smooth, steady automatic acceleration and braking; anti-slip control; an advanced braking system; programmable logic controllers (onboard computers); a controller-area network bus (CAN-bus) (a communications network among systems); and an elevating cab and rotating driving console with a multi-function display.

They could feature electronic steering with the German Goldhofer AST-1X 6x6 A380 tractor achieving a steering angle of 60º on the front axle and, with an optional steerable rear axle, offering front-wheel, all-wheel and diagonal steering modes and the British Douglas-Kalmar TBL600 4x4 / 4x2 A380 tractor offering two-wheel, front and rear, four-wheel and crab steering modes. An over-steer warning system improves safety, e.g. the German GHH Fahrzeug AM500XL 4x4 A380 tractor’s laser-based contact-less Aircraft Moving Over-steering Protection and Indication System (AMOPIS), which controls and continuously reports the position between the tractor and the aircraft and the Goldhofer Overtorque Indication System (GOTIS) on the AST-1X.  The AST-1X uses a specially developed
cardanic suspension so that during towing the pick-up device accommodates nosewheel movement with the minimal introduction of additional forces. The TBL600 accommodates the nosewheel in a cradle and uses a closed-circuit TV system to monitor cradle operation. On the AST-1X a text module informs the driver of the vehicle’s operation. Advanced vehicles also feature greater modularity in their design, which improves their maintainability.

The most powerful of the tractors mentioned, the AST-1X, in its most powerful version, uses two 500kW diesel engines. These tractors, which can also tow wide-body aircraft other than the A380, constitute the top end of their respective manufacturers’ towbarless product ranges and many of their technologies also appear in their smaller, less powerful counterparts. Other A380 towbarless tractors, also fitted with advanced systems, include the American JBT Aerotech Expediter 600 and French TLD TPX-500-MTS. Australia-based Bliss Fox though, produces its A380-capable F1-500 as a conventional (towbar-equipped) tractor, which it identifies as cheaper and simpler and more maintainable than a towbarless model.

All of these vehicles require a driver but Israel Aircraft Industries (IAI) and Airbus will co-develop the Taxibot Dispatch Towing system, which would allow the pilot to control the tow vehicle. According to IAI, Taxibot holds the potential to reduce
annual fuel costs by more than four times, CO2 emissions by more than nine times and noise emissions. Deliveries could
begin by the third quarter of 2011. The pilot will use the aircraft controls in the same way as he would to taxi under aircraft
engine power and the aircraft accommodates the system without modification.
 
Airport Crash Tenders

Among the most technologically advanced of airport vehicles, airport crash tenders lead an airport’s range of aircraft rescue and fire-fighting vehicles (ARFFVs) that also includes conventional fire appliances and rapid intervention vehicles (RIVs). Airport crash tenders require a strong but light body, which in modern vehicles increasingly includes non-metal materials: Austria-based Rosenbauer uses aluminum, glass-reinforced plastic (GRP) and composites in its Panther model and UK-based Carmichael stainless steel, GRP and composites in its Cobra 2.

A rear engine location lowers cabin noise and vibration. Further, manufacturers consider the incorporation of new engine technology, Oshkosh in the US developing the ProPulse Hybrid Electric Drive system for its airport crash tenders. ProPulse improves fuel economy and life-cycle cost and reduces emissions. The diesel engine drives an electric generator, which powers the wheels, removing the need for a torque converter, automatic transmission, transfer case and drive shafts. The system uses ultracapacitors instead of batteries. A regenerative braking mechanism stores energy for future braking.

Vehicle designers seek a low centre of gravity to improve ride stability and a high static tilt angle to increase cornering speed and improve road holding. The Oshkosh Striker airport crash tender uses the TAK-4 independent suspension for a smoother ride, better off-road mobility and braking and longer service life. US-based E-One, manufacturer of the Titan vehicle, developed the Enhanced Ride System (ERS) for improved braking and handling and ride comfort. E-One’s Roll Stability Control (RSC) monitors driving conditions and automatically slows the engine and applies brakes as required. Oshkosh’s Pierce Side Roll Protection System, upon sensing a side-roll, through a solid-state, microprocessor-controlled sensor, tightens the seat belt, lowers and locks the seat and inflates an airbag across the side windows. Manufacturers also stress survivability of the cab in the occurrence of a roll, with as an example the Cobra 2 incorporating a stainless steel triple roll-over cage.

Oshkosh’s All Steer all-wheel steering system feature three steering modes: front steer mode, in which the driver steers traditionally, with rear-wheels locked; coordinated steer mode, for sharp turns, with the front and rear wheels in opposite directions, and crab-steer mode, for the greatest maneuverability at low speeds, with the front and rear wheels in the same direction, allowing sideways motion.
A large windscreen and door windows improves visibility for driver and crew. Carmichael identifies in its Cobra 2 the largest cab on the market, with 1m-wide doors while the doors on the Panther open to 90 º for easy access. Operators also require controls within easy reach. Logic Control System (LCS) technology gives the Panther one-man-operation. Advanced vehicles also use CAN-bus technology. The Striker and, as an option, Titan vehicles feature a Driver Enhanced Vision System (DEVS), and the latter, also as an option, a Monitoring and Data Acquisitioning System (MADAS). The Cobra 2, designed for easy access to engine and pump units, uses a modular body.

Oshkosh also developed the Command Zone computer-controlled,
multiplexed electronics system to operate and diagnose important vehicle systems. Command Zone can give real-time vehicle and engine performance information. E-One’s Vehicle Information Control (VIC) computerized information system allows operation of various systems including live 360º-field-of-view camera inputs. With a modem both Command Zone and VIC allow remote diagnostics.
The fire-extinguishing equipment of more capable airport crash tenders includes a High Reach Extendable Turret, with a nozzle that could penetrate the aircraft fuselage. All four vehicle types above come in 4x4, 6x6 and 8x8 variants. The most powerful of these, the Panther (8x8), uses a 746kW diesel engine, with the Striker (8x8) using a slightly less powerful 708kW diesel engine.
 
Other Vehicle Types

Load handling vehicles that deliver freight to aircraft often employ scissor lifts to reach aircraft cargo doors. Austria-based Catcon developed this type of vehicle further with its SideCat highlifter, which includes the driver’s cab at cabin level to simplify operation. SideCat can transport passengers with wheel chairs or stretchers or VIP passengers with embarkation from ground or other levels, transport freight and serve as a passenger stair extension or a platform for cleaning, catering or servicing. The cabin can reach the upper deck doors of the A380.

Scissor-mounted mobile lounges and screw-mounted plane mates, first conceived decades ago to transfer passengers between terminals and directly to the aircraft, then seemed visionary but failed to prosper, replaced by people movers and moving walkways.

However the logistic problems posed by the continued growth of airports require innovative solutions and these concepts deserve re-consideration. An existing design like the SideCat could undergo development but Canada-based AccessAir
offers a more specialized vehicle, the Plane-Mate 2150.

An Australian innovation, the FOD Boss vehicle-towed airfield sweeper, according to its manufacturer Aerosweep provides cost-effective maintenance-free foreign object debris (FOD) control.

Overall Trends

The need for environmentally-considered operations provides a major impetus to the evolution of the technology of airport
vehicles, for instance the replacement of internal combustion/gasoline/diesel-fuelled engines with new fuels, including hydrogen, and alternative technologies, such as electricity, among smaller, less-powerful tow and other vehicles. Otherwise, as airports
become ever-busier, ground activities continue to become more hectic and attention to safety more crucial, resulting in the
development of technologies to continually track vehicles, such as transponder networks, an example of the pervasive and continuing influence of micro-electronics-based technologies to innovation in airport vehicles.